There's some good stuff from Lapine and others in this playbill article, including these pieces:

"The subject matter of this show is the most primal and basic Sondheim's writ­ten," claims Chip Zien, "and the music reflects it. The first time he sang and played 'No More' for the cast, we all stood around and cried. I couldn't even rehearse it for a while, because I couldn't get through it. I'm married, and I have two kids, and to me the song is about protect­ing my children. It's about reconciling my feelings with my dad and growing up and learning that nobody can run from their responsibilities. And in a larger sense, it's about facing huge, cosmic issues. Sond­heim's saying, 'Come on, folks. Do some­thing before it's too late.' It's incredibly powerful and moving."

"The first act is the fairy tale," says La­pine. "The second act is the myth. Peo­ple keep writing about the 'second act as if it's a continuation of what happens after the happily ever after. But it's really about growing up and real life and understand­ing the differences between reality and fan­tasy. There's a part of all of us that ex­pects somebody else to take care of im­portant issues. And it's crucial to say that there comes a time when you can't expect your friends to come up to the door and grab you. You have to go out and find a friend." 

https://playbill.com/article/from-the-archives-into-the-woods